This invention relates generally to fuel control systems for gaseous fueled engines. More particularly, but not by way of limitation, this invention relates to a prechamber fuel control system for turbocharged, gaseous fueled internal combustion engines.
In the past several years, many regulations have been issued pertinent to the substances emitted by stationary engines that are considered pollutants. Such pollutants include non-methane hydrocarbons (NMHC), oxides of nitrogen (NOx), carbon monoxide (CO), and oxides of sulphur (SOx). In spark ignited, natural gas fuel engines the oxides of nitrogen are normally the highest level emittant and therefore the most difficult to reduce.
It has also been found that the primary engine operating parameter that affects the formation of the oxides of nitrogen is the air fuel ratio. Accordingly, it has been the desire of the engine builders to be able to run the engines on as lean a mixture, that is, on as high an air fuel ratio, as is possible.
Aside from emission control, it is highly desirable to increase the air fuel ratio to as high low a point as is effective to reduce the amount of fuel burned and thus make the engine operation more economical. The natural gas fuels burned in the engines are relatively expensive and, in the next few years, such fuels may become in short supply and thus their conservation is essential. The leaner that the engine can be run the less pollutants generated, the less fuel burned, and the more economical the engine operation.
A manuscript entitled "NOx Reduction on Large Bore Turbo-charge SI Engines" was prepared by J. V. Serve and submitted to the ASME headquarters on Nov. 30, 1981. The manuscript goes into substantial detail regarding the various regulations involving the emittants produced by the engines, their cause, and methods of controlling the same. Further, the manuscript discusses use of the prechamber in natural gas engines and gives an example of a schematic diagram illustrating one form of fuel control for prechambers.
As explained in that paper, the fuel supply to the prechambers is controlled as a function of gas manifold pressure. This is accomplished by branching a line off the manifold through a fixed orifice to a smaller manifold running down the engine with take-offs for each individual cylinder head. While this system will function, a more sophisticated system will provide better prechamber combustion and permit more efficient operation of the engine on higher air fuel ratios. In particular, over most of the engine operating range, the performance is improved if the prechamber is supplied with a mixture of air and gas rather than with gas alone and further improved if the proportion of air and gas can be varied for different operating conditions up to and including the use of pure gas for starting and for full load.
U.S. Pat. No. 4,140,090 issued Feb. 20, 1979 to John E. Lindberg describes an engine utilizing a highly combustible fuel and an oxidizer in a precombustion chamber. Another U.S. Pat. No. 2,435,659 issued Feb. 10, 1948 to C. E. Summers describes a liquid fuel engine, such as an automobile engine utilizing a precombustion chamber.
Therefore, the object of this invention is to provide an improved prechamber fuel supply system that reduces the emittants from the engine, increases fuel efficiency, and permits the engine to operate on a higher air fuel ratio.